Ballooning life expectancies are upending age-old definitions of life stages.

“All the world’s a stage, And all the men and women merely players; They have their exits, and their entrances, And one man in…By Stephen Cave

“All the world’s a stage, And all the men and women merely players; They have their exits, and their entrances, And one man in his time plays many parts, His acts being seven ages.” —Shakespeare, As You Like It

The division of life into age-based roles like childhood and adulthood, or middle age and old age, is a cultural universal—something found in all known human societies.1 It can actually be seen in all complex organisms, since each must find some way of balancing the competing demands of growth, reproduction and survival. The American Sand-burrowing mayfly spends a year growing underwater as a larva, then, all within five minutes, takes on its adult form, mates, lays eggs, and dies. An oak tree, on the other hand, spends decades maturing before it begins its stately annual cycle of acorn-shedding. Despite the differences in speed, life stages are well defined in both cases.

We Homo sapiens are no exception: our life stages are the biological foundation on which our culture is based. From the Bible to Shakespeare, and from bar mitzvahs to celebrating your 21st birthday in a bar, our stories about ourselves revolve around set stages of our life. They shape almost every aspect of our existence: how we see ourselves and how we see others, our plans and our ambitions, and the social structures through which we move.

They also assume one thing: a natural length of a life. But now that is changing, and quickly.

In the developed world, life expectancy has been going up steadily at the rate of two added years every decade. In the United States there were 4 million seniors (age 65 and over) in 1910, while there were 40 million in 2010.2 By 2050, average life expectancy in developed countries is likely to be in the mid-80s,3 and by some calculations, over 90.4

This trend shows no sign of stopping. Some optimists believe it might even accelerate, and that we could soon attain a state of “medical immortality,” completely immune to sickness and infirmity. We wouldn’t really live forever, as we would still be susceptible to catastrophes like being eaten by sharks or blown to pieces, but we could in theory live a very, very long time.

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Many, though, seem to find the prospect of such long lives terrible. In a recent survey, over half of Americans thought that extending people’s lives to 120 years would be bad for society, while the overwhelming majority said they themselves would rather die before they reached 100.5

For advocates of prolonging lifespans, who dream of a future in which we all frolic merrily into our second century, this is a huge frustration. Some of them simply dismiss the skeptical majority as lacking the imagination to make use of the extra decades, or accuse them of being in thrall to a death cult.6 But this underestimates what they are really up against—which is a deeply ingrained idea of what a life should look like, complete with its familiar stages. The question is: how can we adapt our current model of a normal human life without breaking it?

One longevity researcher, Steven Austad, a professor at the University of Alabama at Birmingham, calculated that the average life expectancy of a medical immortal would be around 5,800 years. This figure is based on extrapolating the survival rates for 9-year-olds in the U.S.—chosen because they are least likely to die of illness, as they have survived the diseases of early childhood but not yet fallen prey to those that come with ageing. In societies that are less accident-prone, the average lifespan would be even higher—almost twice as high in safety-conscious Japan. In personal correspondence, Austad wrote to me:

“This is a constantly moving target, but I can tell you how I calculate it. If you look at the annual death rate as a function of age in any human population, it is relatively high around birth, drops to its lowest point around age 8-12, and then increases for the rest of life. I assume that … we completely stopped aging (something I do not consider realistic) and [are] frozen at the health of that age at which death rate is lowest forever after ... With modern medical advances the mortality rate at that ‘minimum mortality age’ keeps inching downward and for every little bit it inches, it has a huge effect. So, for instance, I just calculated life expectancy in the absence of aging if Americans were frozen at the mortality rate (sexes combined) that they had when they were 9 years old (the minimum mortality in 2006). It is now 5,775 years. On the other hand, if I make the same calculation for Japan (2007 data)—the longest-lived country in the world—the answer is 9,901 years because their minimum mortality rate is lower than ours (and achieved at age 9 and again at age 11).”

According to today’s basic model of life, we get an education, start a career and a family, then, when all that is done, enjoy a happy retirement. But now we are living longer, this model is starting to strain.

When pensions were first introduced—by Otto von Bismarck in Germany in 1889—they were for those few who exceeded the 70 years allotted us by the Bible. In the U.S., pensions were introduced as part of Social Security in 1935, when they were given to those over 65. Life expectancy at the time was 60. Pensions were originally intended to keep a handful of survivors out of extreme poverty—but this began to change in the years of prosperity after World War II.7 Today the baby boomers, who grew up in this time of plenty, take it for granted that they should have a prolonged, leisurely retirement—something previously unknown in human history.

With average retirement age in America now at 62 years and life expectancy close to 79, this model is becoming expensive. Already seniors account for over half of welfare spending in the United Kingdom, and approaching half of all federal spending in the U.S. If life expectancy were instead close to 90, then something would have to give. The obvious option is to increase the age of retirement—to at least 70, if not 75, but moves in this direction are so far proving politically unpopular.8

It seems crazy that one age group has to simultaneously build a career, raise children and financially support a growing number of older people who do nothing.

Increasing the retirement age would also cause other problems, such as fewer jobs available for young people, who already suffer disproportionately from unemployment. Not only would seniors likely have the best positions—the directorships and professorships—but those fields dependent on fresh ideas might stagnate. If, as Max Planck said, science advances one funeral at a time, then postponed funerals means slowed progress.

Postponing retirement also means working longer. Some scholars are already talking about the “redistribution of work”—spreading work more evenly across people of different ages.9 Longer lives, argue the demographers James W. Vaupel and Elke Loichinger, will mean we need more “life-course flexibility.” It seems crazy that one age group has to simultaneously build a career, raise children and financially support a growing number of older people who do nothing, even though many are willing and able to work. (As a father of three with a full-time working wife, this is an argument with which I can identify.)

Vaupel and Loichinger therefore suggest that part-time work should become the norm, both for younger people who might also have child-rearing or educational commitments, and for older people, who are still fit and won’t be able to rely on generous pensions for their livelihood. This trend is already visible and a recent British Government report suggests it is set to continue, with, in particular, more men opting for part-time work as they increasingly take on child-care duties.10

As lifespans become much longer, we might need to take this idea one step further. Instead of a linear progression from education through employment to retirement, we could instead imagine a cyclical approach. Acknowledging that over a long lifespan, our interests and needs will change, we could have repeated phases of training, work and break. A person might expect to have three or four different careers over the course of her long life, with gaps for raising a family, traveling the world or just tending the garden.

Such a cyclical approach would solve many problems. If everyone, even the most senior, was expected to move on after a set time, then we wouldn’t need to worry about the top jobs being hogged by an ageing few. The professor of Greek would step down, and—perhaps after a few years of well-earned rest sailing the Aegean—might retrain as a software engineer. As well as allowing us to explore new interests, such periods of retraining would also ensure our skills did not become redundant. They might also keep our motivation for work high, in a way that the prospect of a century sitting at the same desk might not.

If the nuclear family still existed, it would be recognized as a temporary phenomenon; one phase of many in the lives of those involved.

This trend too is already underway: One survey estimated that 9 million Americans aged between 44 and 70 are already engaged in second careers, and 31 million more are interested in pursuing one.11 These workers are motivated by the desire to stay active, to keep learning, and to help others. After a first career spent in pursuit of money or status, many are choosing a second that is focused on giving back, such as teaching or healthcare.12

Along with abandoning the idea of a job-for-life, we might have to rethink other currently lifelong institutions, such as marriage. When we stick around a lot longer, the idea of a single partner for life looks increasingly implausible. A recent study in Canada showed that we alter our reproductive behavior in line with our life expectancy, just as life history theory would suggest: The longer-lived get married later and have children later, but are also more likely to divorce.13 Consciously or unconsciously, when we have more years ahead of us we become more likely to take the risk of trying for a new, happier arrangement.

As people are anyway divorcing more frequently as they live longer, it might make sense to save them the pain of broken promises by replacing “till death do us part” with a time-limited marriage contract. Jonathan Swift presciently suggested something like this in his 1726 novel Gulliver’s Travels, wherein the undying ‘struldbrugs’ automatically have their marriages annulled as soon as they’ve both turned 80. In what might be a sign of things to come, the idea of time-limited marriages was recently proposed by legislators in Mexico City, although it was blocked by conservatives.14 Some relationships counselors are now actively exploring this: in their book The New I Do, for example, Susan Pease Gadoua and Vicki Larson propose a range of different kinds of contract, from the short-term “starter marriage” to the “parenting marriage” for the duration it takes to raise children.

If the nuclear family then still existed, it would be recognized as a temporary phenomenon; one phase of many in the lives of those involved—particularly if anti-ageing breakthroughs also delayed menopause, allowing women to have children later. We are currently seeing rising numbers of non-traditional family forms; when siblings, half-siblings and step-siblings are increasingly born decades apart from each other, these patchwork families will become ever more complicated.15

Changes like these might seem unnatural at first, but in a sense they are the opposite. The strand of biology known as life history theory predicts both that each species will have a basic life plan, and also that it will adapt this plan to its particular environment. When mortality rates are high, for example, fruit flies accelerate their sexual activity; whereas with fewer predators and parasites around, they take their time.16 So it is natural that we too should adapt our life plan as our environment becomes more benign, with ample nutrition and medical technology giving us a good chance of living to a very ripe old age.

These adaptations are already underway. For some this is unsettling, as ancient practices are called into question. But with a little imagination, we can see this as an opportunity for reinvention and renewal; to have what many have long dreamed of—a second, third, or fourth shot at life.

Stephen Cave is a philosopher and author of Immortality: The Quest to Live Forever and How it Drives Civilization.

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